Looks like the logic inside modern Intel CPUs are too aggressive in pre-loading cache data and forget to check security boundaries... loading data from kernel (or possible other code space) into a region that malicious code could have access too:
https://www.theregister.co.uk/2018/01/02/intel_cpu_design_flaw/
(sourced from this conversation: https://www.reddit.com/r/linux/comments/7npnd4/kernel_41411_is_out_with… )